Did not notice this before the update but now I'm seeing disadvantage on attack roles when enemies are prone.
This is likely just the basic D&D 5e rule. Where were you attacking from?
The description for the Prone condition states:
An Attack roll against the creature has advantage if the attacker is within 5 feet of the creature. Otherwise, the Attack roll has disadvantage.
So, if you were standing next to them and beating on them with a melee weapon, you should get advantage. If you're using any kind of ranged weapon (bow, cantrip) then the disadvantage is correct.
Glad you brought the source as well, because it is interesting that people can go to the books and check the rules out.
i just used spirtial weapon to attack a prone creature, when the attack was initiated the weapon was a couple of squares away and the hover-over said the attack would be at disadvantage, however, once the weapon got to the target the attack was made at advantage, so it works correctly, but the initial attack setup info needs to be fixed
yellow flower of courage